PURPOSE: To obtain the titled composition giving a cured product having excellent flexibility, alkali resistance, water resistance and mar resistance, and useful for impregnation, casting, lamination and coating use, by compounding an epoxy resin, a diester dicarboxylic acid and a polycarboxylic acid anhydride.

CONSTITUTION: The objective composition is prepared by compounding (A) an epoxy resin (e.g. polyglycidyl ether of polyphenol, etc.), (B) a diester dicarboxylic acid of formula [R1 and R3 are bivalent aromatic group or (cyclo)aliphatic group; R2 is H or methyl] and (C) a polycarboxylc acid anhydride (e.g. phthalic anhydride). The amounts of the components (B) and (C) are selected to be 0.15W 0.5 equivalent and 0.5W0.85 equivalent per 1 equivalent of the component (A), respectively. The component (B) is preferably prepared by reacting e.g. methyl hexahydrophthalic anhydride, etc. with triethylene glycol, etc. at a molar ratio of 2:1.